At the present time polychlorinated biphenyls, formerly widely used in transformers and capacitors, are no longer being produced or used in the United States due to environmental concerns. They have been replaced with silicone fluids and with hydrocarbon fluids such as a fluid described in U.S. Pat. No. 4,082,866 a mixture of naphthenic hydrocarbons and hydrogenated paraffins. Both of these fluids meet NEC code requirements for fire resistance with a 300.degree. fire point and no propagation of the flame, and both fluids are environmentally acceptable. However, these fluids, especially the silicone fluids, are quite expensive.